We recommend ordering enough center sections to construct a deep well hand pump long enough to reach just below the depth of your existing submersible but at least 10 feet from the bottom of your well. The small diameter of the pipe allows you to do this, unlike most other hand pumps on the market. It's best to draw from the water surrounding your existing submersible due to the constant draw of fresh water.
If you don't know the debth of your submersible, you can usually find it online. Most states have well water log databases that can be searched for information about your well when it was drilled. Due to regulations regarding the drilling of water wells, many states require the well driller to attach a well ID or tag to the top of the well casing which uniquely identifies your well. If you know the contractor who drilled the well you can call directly and ask about the well specifics.